Project Summary/Abstract There remains a fundamental gap in our understanding of how PTEN maintains a tumor-suppressive physiological level, and how this level becomes deregulated in cancer which renders PTEN biology in human cancer largely incomprehensible. Our long-term goal is to fill that gap, and thereby enable the development of novel targeted therapeutics for treating cancer. The specific objective of this application is to identify novel regulatory mechanisms of PTEN signaling for preventative and therapeutic purposes. Our central hypothesis is that PTEN is auto-regulated by feedback mechanism, and that this novel PTEN ?integrated circuit? plays an important role in tumor suppression and could offer exciting new options for cancer therapy. This hypothesis has been formulated on the basis of preliminary data produced in the applicant's laboratory. The rationale for the proposed research is that once we know how PTEN dosage is regulated in cancer, the activity of PTEN modulators can likely be manipulated pharmacologically to restore PTEN expression, resulting in new and innovate approaches to prevention and therapy. Guided by strong preliminary data, we will test our hypothesis by pursuing three specific aims: 1) To define, in knockout mice, the role of a novel physiological deubiquitinase (DUB) for PTEN in tumorigenesis; 2) To determine the molecular basis of the crosstalk between the DUB and PTEN-PI3K-AKT networks; and 3) To assess the benefit of PTEN restoration induced by pharmacological activation of DUB as a promising therapeutic option. Under the first aim, a series of PTEN specific DUB knockout mouse models, which have been already created and found feasible by the applicant, will be characterized for tumorigenesis. Under the second aim, the applicant's identification of PTEN specific DUB as a novel, essential downstream target of the PI3K-AKT pathway will be further verified to explore a possible link between the DUB and PTEN-PI3K-AKT networks in tumorigenesis. Under the third aim, a preclinical evaluation of an already proven agent activating PTEN DUB and combined therapy with inhibitors of PI3K or PARP will be undertaken in genetic models of cancer. This approach is innovative in that it explores the regulation of PTEN dosage and activity by a novel, critical PTEN feedback mechanism as a source of exciting new therapeutic opportunities, and the applicant is confident the resulting findings will open new horizons for therapeutic research. The proposed work is also significant in that it is expected to vertically advance and expand understanding of how PTEN-integrated signaling networks are deregulated in many human cancers. Ultimately, therapeutic interventions designed to advance the PTEN feedback mechanism could prove useful in blocking cancer development, and so hold great preventative and therapeutic promise.